Hot-melt adhesives recently employed for rationalization of sewing works have indeed radically rationalized sewing works and are currently in wide use. The hot-melt adhesives so far in use include polyethylene-based, polyamide-based, plasticized polyvinyl chloride-based, polyvinyl acetate-based and polyester-based ones, among others. However, they respectively have problems. Thus, 1 polyethylene-based adhesives are unsatisfactory in bonding strength, feeling, and resistance to dry cleaning; 2 polyamide-based adhesives are sufficient in bonding strength and resistance to dry cleaning but unsatisfactory in feeling and resistance to laundering; 3 plasticized polyvinyl chloride-based adhesives are sufficient in feeling and resistance to laundering but unsatisfactory in resistance to dry cleaning, and they have other problems in that they are subject to changes in bonding performance, feeling and other properties with the lapse of time due to migration of plasticizer during storage of interlining cloths; 4 polyvinyl acetate-based adhesives are satisfactory in feeling but insufficient in resistance to laundering and to dry cleaning; and 5 polyester-based adhesives are satisfactory in bonding strength and resistance to laundering but insufficient in resistance to dry cleaning.
To overcome the above problems, a hot-melt adhesive comprising a thermoplastic polyurethane resin powder has been proposed (Japanese Kokoku Publication Sho-63-15930; Japanese Kokai Publication Sho-55-110173). However, this polyurethane resin powder-based adhesive has problems in that it is insufficient in hot-melt property, hence its bonding property cannot be improved to a satisfactory extent.
On the other hand, the slush molding technique has recently acquired wide popularity in the manufacture of automotive upholstery, among others, since products complicated in shape and form (undercuts, deep formings, etc.) can be molded with ease and uniform thicknesses and good yields can be obtained by this technique. Plasticized polyvinyl chloride (hereinafter briefly referred to as PVC) powders are mainly used in such applications.
However, because any plasticized PVC contains a low molecular weight plasticizer in a large proportion, it tends to cause various problems due to aging, e.g. fogging of the windshield of a car due to formation of an oil film interfering with the driver's vision by volatilization of the plasticizer, loss of matting and a soft feel of shaped articles due to migration of the plasticizer to the surface, and yellowing of the articles due to degradation of the PVC with time.
Modified PVC compositions prepared by incorporating a flexible thermoplastic polyurethane resin are known as materials for providing a soft feel without using any low-molecular plasticizer (e.g. Japanese Kokoku Publication Sho-53-29705, Sho-59-39464 and Sho-60-30688). In each modification, however, the base resin is PVC and therefore the problem of degradation of articles with time has not been resolved as yet. Attempts have been made to improve such problems and obtain products with desired physical properties by using polyurethane resins alone (e.g. Japanese Kokai Publication Hei-02-38453 and Hei-03-97712). However, the resin powders used therein have poor hot-melting properties, hence can hardly give molded sheets with good surface smoothness, rendering it difficult to use it in slush molding.
Accordingly, it is an object of the present invention to provide a hot-melt resin composition which shows good (sharp) hot-melting property and which, when used as an adhesive for interlining, shows good adhesiveness, flexibility (feel), resistance to laundering and resistance to dry cleaning and, when used as a slush molding material, gives molded sheets with good smoothness, flexibility, antifogging property and resin strength and to provide a hot-melting property improving agent to be used in said composition.